1. Field of the Invention
The present invention relates to a method and an apparatus for working a burred portion, i.e., a portion which is formed into a projecting edge, of a metallic plate. It relates, in particular, to a method and an apparatus for additionally or further working a sheer drop or roll over which occurs in the form of a sink or rounded edge at the base of a burred portion of a relatively thick metallic plate as well as working an irregular surface at a front end of the burred portion.
2. Description of Related Art
An art of further working a metallic plate to make the shape of the burred portion into a desired one is known for example in Japanese Published Unexamined Patent Application No. 260631/1988. In the art disclosed therein, a workpiece made of a relatively thin metallic plate is held in a pinching manner between a die which is urged by a spring and a stopper. A burred portion is formed by means of this die and a punch which is arranged to pass through the stopper. In a condition in which the workpiece, the die, the stopper and the punch are closely held together, the burred portion is pressed against a pressurizing element which is stationarily disposed opposite the burred portion, thereby performing the further working of the burred portion.
In this conventional art, the frictional force to be generated by the urging pressure of the spring is used as a means of holding the workpiece in position. It follows that the workpiece is likely to be moved laterally at the time of correcting or further working the burred portion. This tendency of lateral movement is more conspicuous when a larger pressing force is required for further working a relatively thicker workpiece. As a result, the position of the burred portion relative to the periphery of the workpiece is likely to become inaccurate.
The present invention has an object of providing a method and an apparatus for working a burred portion of a workpiece in which the burred portion which is free from shear drop and is accurate in its front end shape can be formed in a correct position relative to the periphery of a plate or a plane portion, as opposed to the burred portion, of the workpiece.
According to one aspect of the present invention, the foregoing and other objects are attained by a method of working a burred portion comprising the steps of: at least partially punching a periphery of a workpiece, which has already been subjected to burring, by a periphery punch and a periphery die; and further pressing the burred portion by the periphery die and a die surface including an annular portion which opposes the periphery punch while restricting a lateral movement of the workpiece by the periphery die.
In accordance with another aspect of the present invention, the foregoing and other objects are attained by a method of working a burred portion comprising the steps of: feeding into a periphery die a workpiece which has already been subjected to burring and a periphery of which has already been punched into a predetermined dimension; and pressing the burred portion by an upper punch and a die surface including an annular portion which opposes the upper punch while restricting a lateral movement of the workpiece by the periphery die.
In accordance with still another aspect of the present invention, the foregoing and other objects are attained by an apparatus for working a burred portion comprising: a metallic mold having a periphery die and a periphery punch which are arranged to at least partially punch a periphery of a workpiece which has already been subjected to burring; a lifter which is disposed inside the periphery die so as to be movable up and down relative to the periphery die; and further working means for further working the burred portion into a shape and dimension to those of a final product of the workpiece while restricting a lateral movement of the workpiece by the periphery die.
In accordance with a still further aspect of the present invention, the foregoing and other objects are attained by an apparatus for working a burred portion comprising: a metallic mold having a periphery die and an upper punch, the periphery die being arranged such that a workpiece, which has already been subjected to burring and a periphery of which has already been punched into a predetermined dimension, is fed thereinto; a lifter which is disposed inside the periphery die so as to be movable up and down relative to the periphery die; and further working means for further working the burred portion into a shape and dimension of those of a final product of the workpiece while restricting a lateral movement of the workpiece by the periphery die.
Preferably, the further working means comprises a pilot pin which is projectingly fixed to a lower end of the periphery punch or the upper punch; and a knockout which is disposed in a recess in the lifter so as to be movable up and down, the knockout having an annular portion on an upper edge thereof. The pilot pin has an outer diameter substantially equal to an inner diameter of the burred portion and the annular portion has an inner diameter substantially equal to the outer diameter of the pilot pin and a thickness substantially equal to a thickness of the burred portion of the final product. An upper surface of the annular portion is arranged to pressingly receive a front end of the burred portion.
According to still another aspect of the present invention, the foregoing and other objects are attained by an apparatus for working a burred portion comprising: a metallic mold having a periphery die and a periphery punch which are arranged to at least partially punch a periphery of a workpiece which has already been subjected to burring; a lifter which is disposed inside the periphery die so as to be movable up and down relative to the periphery die; and a central member disposed inside the lifter. The central member comprises an upper cylindrical portion for receiving therethrough the burred portion of the workpiece and a peripheral annular portion having an upper flat surface for receiving thereon a front end of the burred portion such that further working of the burred portion can be carried out while restricting a lateral movement of the workpiece by the periphery die.
According to still further aspect of the present invention, the foregoing and other objects are attained by an apparatus for working a burred portion comprising: a metallic mold having a periphery die and an upper punch which are arranged to receive therein a workpiece which has already been subjected to burring and a periphery of which has already been punched into a predetermined dimension; a lifter which is disposed inside the periphery die so as to be movable up and down relative to the periphery die; and a central member disposed inside the lifter. The central member comprises an upper cylindrical portion for receiving therethrough the burred portion of the workpiece and a peripheral annular portion having an upper flat surface for receiving thereon a front end of the burred portion such that further working of the burred portion can be carried out while restricting a lateral movement of the workpiece by the periphery die.
Preferably, the cylindrical portion of the central member has an outer diameter substantially equal to an inner diameter of the burred portion of a final product of the workpiece. The peripheral annular portion has a thickness substantially equal to the thickness of the burred portion of the final product.
According to the above-described method of one aspect of the present invention, since the burred portion is further worked while the periphery of the workpiece is being restricted in its lateral movement by the periphery die, the position of the burred portion relative to the periphery of the workpiece is held constant.
According to the above-described method of another aspect of the present invention, the workpiece which has already been punched in its periphery is fed into the periphery die and the further working of the burred portion is carried out while restricting the lateral movement by the periphery die. Therefore, the position of the burred portion relative to the periphery of the workpiece is also held constant.
By the above-described further working, the radius of curvature of a shear drop which was formed at a base portion of the burred portion is shortened and the front surface thereof is made to a predetermined shape.